clear;
pollen = imread('Fig3.10(b).jpg');
u = double(pollen);
[nx ny] = size(u)
nshades = 256;
r1 = 80;  s1 = 10;   % Transformation by piecewise linear function.
r2 = 140; s2 = 245;
for i = 1:nx
    for j = 1:ny
        if (u(i,j)< r1)
            uspread(i,j) = ((s1-0)/(r1-0))*u(i,j)
        end
        if ((u(i,j)>=r1) & (u(i,j)<= r2))
            uspread(i,j) = ((s2 - s1)/(r2 - r1))*(u(i,j) - r1)+ s1;
        end
        if (u(i,j)>r2)
            uspread(i,j) = ((255 - s2)/(255 - r2))*(u(i,j) - r2) + s2;
        end
    end
end
hist= zeros(nshades,1);
for i=1:nx
    for j=1:ny
        for k=0:nshades-1
            if uspread(i,j)==k
                hist(k+1)=hist(k+1)+1;
            end
        end
    end
end
plot(hist);
pollenspreada = uint8(uspread);
imwrite(pollenspreada, 'pollenspread.jpg');